The underlying mechanisms by which sensations are transmitted from dentin are not fully understood. The theory that has received the greatest acceptance is known as the "hydrodynamic theory". This theory states that dentinal pain is caused by the movement of fluid in dentinal tubules which induces a depolarization of the sensory nerve ending localized near the pulp dentin border. The proposed studies will be conducted on anesthetized cats and examine this issue. Experiments will be conducted that examine the relationship between fluid movement within the dentinal tubules and intradental nerve activity (INA). The ability of various treatments (i.e. smear layer, potassium oxalate, potassium nitrate) to alter this relationship will also be examined. In addition, the mechanism(s) by which these treatments alter the relationship between dentinal fluid movement and INA will be examined. It is hypothetized that a direct relationship between INA and fluid movement will be demonstrated. In addition, it is proposed that the presence of the smear layer in cavity preparations or the application of potassium oxalate to cavity preparations will attenuate INA responses to grade stimuli which will alter fluid movement by obstructing dentinal tubules. It is also proposed that potassium based salts will directly impair INA responses when applied to deep cavity preparations irrespective of their abilities to alter dentinal tubule conductance. A major strength of this proposal is that both INA responses and fluid conductance will be measured in the same preparation in vivo.